The ragwort flea beetle, Longitarsus jacobaeae (Waterhouse) (Chrysomelidae) is considered to be the most important biological control agent for the suppression of tansy ragwort in the Mediterranean habitats of California, Oregon and Washington. However, introductions of ragwort flea beetle into areas east of the Cascade Mountains have repeatedly failed, presumably due to reproductive asynchrony with cold continental climates. An infestation of tansy ragwort discovered in northwest Montana in the 1990s has been the impetus to explore a cold adapted strain of the ragwort flea beetle within it's native range. This is the first detailed report of the bionomics of naturally occurring populations of ragwort flea beetles from central Europe. Adult L. jacobaeae emergence and oviposition, along with larval feeding and development were observed at four field sites in Switzerland. Adult flea beetles emerge in late June and start oviposition after two weeks. Eggs diapause through the winter and hatch in early spring. Larvae initially feed in the leaves and then move to the root crowns to complete their development. Pupation occurs in the soil after the larvae leaves the plant. Additional laboratory experiments were conducted to measure oviposition, egg diapause, eclosion and subsequent larval development under controlled conditions. These data were compared with laboratory and field data of the Italian strain of ragwort flea beetle collected from Mediterranean environments in Oregon. We found that populations of L. jacobaeae from the mountainous regions of Switzerland have several phenological adaptations to cold climates that are absent in the populations found in Oregon.